Question

When 8.1 g of an unknown non-electrolyte is dissolved in 50.0 g of carbon tetrachloride, the boiling point increased by 3.67 degrees C. If the Kbp of the solvent is 4.95 K/m, calculate the molar mass of the unknown solute.

Answer 1

218.3 g/mol

Step-by-step explanation:

Boiling point elevation occurs when a solute is added to a solvent increasing the boiling point of the solution with regard to the pure solvent.

The law is:

ΔT = Kb×m×i

Where ΔT is change in temperature (3.67°C), Kb is the boiling point constant of the solvent (4.95°C/m), m is molality of the solution and i is Van't Hoff factor (1 for a non-electrolyte).

3.67°C = 4.95°C/m×m×i

0.7414m = molality of the solution (Moles solute / kg solvent).

As the mass of the solvent is 50.0g = 0.0500kg:

0.7414m = Moles solute / 0.0500kg

0.0371 = moles of solute

As the mass of the solute is 8.1g, molar mass of the solute (Ratio between mass in g and moles) is:

8.1g / 0.0371mol =

218.3 g/mol